1. Field of the Invention
The present invention relates to an electronic still video camera having an electro-developing recording medium in which an optical image obtained through a photographing lens system is electronically and directly recorded and developed as a visible image in very little time.
2. Description of the Related Art
Conventionally, silver halide photographic material is generally used as a material for recording an optical image. Silver halide photographic material has high optical sensitivity and high resolution, and the economical efficiency thereof is excellent. However, silver halide photographic material has drawbacks in that not only is the developing process cumbersome but also a visible image cannot be obtained at the same time as photography. A dry-type developing method has been developed to simplify the developing process. However, simultaneous development in which a visible image is obtained upon photography is impossible in the dry-type developing method.
On the other hand, as non-silver-halide photographic materials, there are known electrophotographic materials, diazotype photographic materials and free-radical photographic materials and so on. In these materials, however, there is no material which has advantageous characteristics like silver halide photographic material, while being able to simultaneously develop and keep a visible image. Note that, electrophotographic materials have been used mainly in copying machines, since they can perform dry-type development and can simultaneously develop an electrostatic latent image, which is obtained by exposure, using toner.
In such electrophotographic materials, recently, a photographic material has been developed, in which an optical image can be electronically and directly recorded and developed as a visible image in no time, the image so developed being similar to one obtained in a silver halide photographic material. A recording medium formed of such a recording material, in which a visible image is electronically and directly recorded and developed, is referred to as an electro-developing recording medium hereinafter.
For example, Japanese Unexamined Patent Publication No. 5-2280 and U.S. Pat. No. 5,424,156 disclose one type of electro-developing recording medium comprising an electrostatic information recording medium and an electric charge keeping medium. The electrostatic information recording medium includes a photoconducting layer and an inorganic oxide material layer, and the electric charge keeping medium includes a liquid crystal display, both the mediums being combined to face each other with a small gap therebetween. In use, a voltage is applied between the electrostatic information recording medium and the electric charge keeping medium, and an optical image is formed on the electrostatic information recording medium during the application of the voltage. An electric charge distribution is produced over the electrostatic information recording medium in accordance with a light intensity distribution of the optical image formed thereon, so that the intensity of an electric field acts on the liquid crystal of the electric charge keeping medium in accordance with the electric charge distribution. Thus, an image derived from the optical image is reproduced in the electric charge keeping medium as a visible image. Namely, as soon as the optical image is formed on the electrostatic information recording medium, the image is developed in the electric charge keeping medium.
When the electric charge keeping medium is constituted as a memory type liquid crystal display, the developed visible image can be kept therein even if the electric field is eliminated from the electro-developing recording medium. In the memory type liquid crystal display, the developed image can be erased by heating it at a given temperature. In this case, the same electro-developing recording medium can be repeatedly used for photographing.
In an electronic still video camera having the electro-developing recording medium, there may be provided an image reader comprising a CCD line sensor for electronically reading image signals from a developed image of the electro-developing recording medium, and the read image signals obtained from the CCD image sensor may be processed in various manners. For example, the read image signals may be stored in a second recording medium such as an IC memory card, a floppy disk, a hard disk or the like. Also, the read image signals may be transferred from the camera to an external processing device such as a computer, a TV monitor and so on.
Also, in such an electronic still video camera, it is desirable that the developed is erased after the read image signals are stored in the second recording medium, so that the same electro-developing recording medium can be repeatedly used for photographing. In this case, the developed image cannot erased from the electro-developing recording medium by an erroneous switching operation of the camera.
On the other hand, when the electronic still video camera is arranged such that a developed image can be thermally erased from the electro-developing recording medium, it is desirable that the thermal erasing mechanism is incorporated in the camera without a bulkiness of the camera.
Furthermore, in the electronic still video camera, when the image signals read from the developed image of the electro-developing recording medium are transferred from the camera to the external device such as a computer, a TV monitor or the like, the transfer of the image signals to the external device should not be executed without establishing a connection between the camera and the external device, so that an electric poser source of the camera can not be wastefully consumed. On the other hand, the electric power source of the camera should be arranged such that the complete transfer of the image signals to the external device can be ensured without interrupting the transfer of the image signals due to a consumption of the power source.